1. Field of the Invention
This invention relates to a tire internal pressure control apparatus for tired vehicles, and more particularly to a tire internal pressure control apparatus for a tired electric train which can generate an alarm at a driver's seat when the internal pressure of the tire is decreased to a value which is lower than a given value.
2. Description of the Prior Art
In the above mentioned kind of the tire internal pressure control apparatus heretofore proposed, the internal pressure of the tire is supplied through a rubber hose to a pressure indicator which is provided with a normally open pressure switch. When the internal pressure of the tire is decreased, the normally open pressure switch is closed to generate an electric signal which is transmitted through a slip ring to a non-rotational side of the vehicle, that is, a vehicle body side. At the vehicle body side, the electric signal received is supplied through a relay to a display device at a driver's seat, thereby giving an alarm.
In such conventional alarm apparatus, use is made of the slip ring for the purpose of transmitting the signal delivered from the rotational side of the vehicle, that is, a rotational body to the stationary side thereof, that is, the vehicle body. As a result, a brush of the slip ring becomes considerably worn and hence its slip ring must be changed to a new one after the lapse of a given time and the apparatus required much maintenance. In addition, if water penetrates into the slip ring, an erroneous signal is frequently generated and hence the apparatus becomes unreliable in operation. Moreover, the slip ring must be removed and mounted everytime the tires are changed in positions or the tire is changed into a new one. As a result, the apparatus is troublesome in operation and the slip ring in itself is considerably expensive.
Another tire internal pressure alarm apparatus which does not make use of a slip ring but makes use of a non-contact electrical coupling for the purpose of transmitting signals from the rotary body of the vehicle to the stationary body thereof has also been proposed.
But, such kind of conventional tire internal pressure alarm apparatus makes use of an integrated circuit as a signal treatment logical circuit. The integrated circuit is very expensive and hence the apparatus as a whole becomes considerably expensive. In addition, the use of the integrated circuit makes the circuit complex in construction and provides the disadvantage that the apparatus is frequently subjected to faults, erroneous operation or the like.
Moreover, such conventional apparatus cannot generate an alarm when the apparatus in itself becomes defective.